The present invention relates to an air track system and more particularly to an air track edge guide construction useful in transporting reticles for integrated circuit microlighography.
Air track systems of various types have been devised for transporting many different kinds of articles. In particular, air tracks have found extensive usage in the semiconductor industry for transporting silicon wafers from magazines to work stations and back and also between work stations. In general, these air track transporting systems employ an essentially flat horizontal surface incorporating a number of ports for introducing an airflow which establishes an air cushion under the articles to be transported. Usually the article being transported is directly or mechanically constrained to the desired path although various self-centering systems have been devised for causing light objects, such as semiconductor wafers, to follow the track without direct mechanical constraint.
In some systems where it has been desired to constrain the path of a larger article without contact, air bearings have been provided along sidewalls of a track as well as under the track. In such cases the sidewalls act in generally the same manner as the track bed; that is, an air cushion is generated between the article and a wall, and the air jets creating the cushion are generally directed at the article, i.e. laterally in the case of the sidewalls. In the case of relatively thin articles, however, e.g., reticles or semiconductor wafers, such laterally directed air jets have not proven particularly effective.
Particularly in the case of reticles, it is typically desired to precisely control the movement and location of the reticles since, at the work station, the reticle must be very precisely positioned and aligned before it is to expose a pattern on the semiconductor wafer as part of the photolithographic process. It is also highly desirable to avoid, wherever possible, direct physical contact with a reticle since any abrasion at all may generate microscopic particles of dust which, if they end up on the surface of the reticle, can cause imperfections in the semiconductor devices being manufactured and thereby significantly reduce the yield of good integrated circuit devices from the semiconductor wafers.
Among the several objects of the present invention may be noted the provision of air track apparatus for transporting articles without direct mechanical contact; the provision of such an apparatus which is suitable for transporting reticles used in the microlithography of integrated circuit manufacture; the provision of such a system which precisely controls the location and orientation of the articles being transported; the provision of such an apparatus which will guide an article from one side of an air track on which the article is being transported; the provision of such apparatus which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.